Optical filters are commonly used in a wide variety of applications. For example, optical filters are used to provide separate optical “channels” in optical fiber networks. Optical filters are also used to monitor the spectral emission from the power plants and engines to provide a level of combustion monitoring and control. Optical filters can also be used in biological particle identification systems to provide spectral resolution of the fluorescence needed for high levels of discrimination of biological materials. These are just a few of the many applications for optical filters.
Many optical filters are formed from thin films that reflect or transmit a narrow band of wavelengths. In many cases, such filters are constructed from several hundred layers of stacked narrow band filters, which collectively reflect or transmit a narrow band of wavelengths. Arrayed waveguide gratings are also commonly used. A limitation of many of these filters is that they are not wavelength tunable. That is, the operative wavelength cannot be dynamically changed during operation to select a different optical wavelength.
Biological or inorganic particle identification systems identify the size and class of particles in air via scattered light and intrinsic ultraviolet fluorescence measurements. These system are useful as early warning sensors in biological warfare (BW) agent attacks either in an urban area or on a battlefield. Present day systems, such as a fluorescence aerodynamic particle sizer are large and power hungry, and are not portable. Smaller and more lightweight systems are desired for both portable applications and for incorporation into larger, more complex systems for building protection and battlefield BW agent detection systems.
Optical filters are combined with detectors for measuring the amount of fluorescence passing through the filters. Some detectors have a limited bandwidth of detection that is not as great as the bandwidth desirably passed by the filter. There is a need for an improved detector that can detect a larger bandwidth passed by the filter.